The present invention relates to diamond-like glass, articles deposited with diamond-like glass, methods of making diamond-like glass, and apparatus for depositing diamond-like glass.
In recent years, various diamond-like thin films have been created which allow for the creation of hard deposits on various substrates. For example, U.S. Pat. No. 5,466,431 teaches diamond-like metallic nanocomposites, which are diamond-like interpenetrating networks of carbon stabilized by hydrogen and a silicone glass-like network stabilized by oxygen. Such nanocomposites are sometimes referred to as DYLYN, and are manufactured by Advanced Refractory Technologies of Buffalo, New York. Although DYLYN nanocomposites are useful for some applications, they have limitations making them unsuitable for many applications. For example, DYLYN is relatively absorbent to UV-visible light, which makes it unsuitable for applications where transparency of such light is necessary. Furthermore, DYLYN has a relatively high refractive index on the order of 1.7 to 2.5, which makes it of limited use when reflective losses must be limited, such as for anti-reflective coatings.
Similarly, various plasma deposited silicon oxide thin films have been generated. Such films, generically represented as SiOx are usually formed from silane/oxygen or silane/nitrous oxide mixtures and do not contain carbon. Again, although useful for some applications, these SiOx films are typically substantially optically absorbent and are also relatively brittle and prone to flex cracking. In addition, SiOx films are usually deposited at high temperatures in order to avoid formation of a porous film. Although these high temperatures can create dense films, they also limit the type of substrates that can be used without being degraded by heat.
Another type of hard thin film is plasma polymerized organosilicone (PPO). Some PPO is formed by fragmentation and deposit of precursor molecules in a plasma to form a plasma polymer that is deposited on a grounded electrode. However, this PPO often does not adequately cover and fill surface topographical features, and the size of the plasma polymer precludes some lateral mobility as they condense on the substrate. Lateral mobility refers to the ability of atoms deposited on a surface to move a slight distance from the spot where they first land, allowing them to fill holes and provide a more uniform coating. Other PPO includes condensed monomer molecules that are polymerized by using various energy sources, such as ultraviolet light or e-beam radiation. Again, although this PPO has some uses, it often does not form densely packed, random films, and therefore is not as hard or homogenous as desired for some applications.
While each of the aforementioned compositions has specific utility, a need exists for an improved hard thin film that can be deposited onto a variety of substrates, preferably including heat sensitive substrates. The film is also preferably flexible so that it can be applied to a wide variety of substrates, including flexible substrates. In addition, the thin film preferably allows transmission of most light, including ultraviolet light. Finally, the film preferably has diamond-like hardness and a minimum of porosity.
One aspect of the present invention is directed to an improved thin film having use in many different applications. The improved thin film is a diamond-like glass, and may be applied to various substrates. Other aspects of the invention aredirected to articles having a diamond-like glass film, methods of making the articles, and apparatus for making the film and articles.
The diamond-like glass (DLG) of the invention comprises a carbon-rich diamond-like amorphous covalent system containing carbon, silicon, hydrogen and oxygen. The DLG is created by depositing a dense random covalent system comprising carbon, silicon, hydrogen, and oxygen under ion bombardment conditions by locating a substrate on a powered electrode in a radio frequency (xe2x80x9cRFxe2x80x9d) chemical reactor. In specific implementations, DLG is deposited under intense ion bombardment conditions from mixtures of tetramethylsilane and oxygen. Typically, DLG shows negligible optical absorption in the visible and ultraviolet regions (250 to 800 nm). Also, DLG usually shows improved resistance to flex-cracking compared to some other types of carbonaceous films and excellent adhesion to many substrates, including ceramics, glass, metals and polymers.
DLG contains at least about 30 atomic percent carbon, at least about 25 atomic percent silicon, and less than or equal to about 45 atomic percent oxygen. DLG typically contains from about 30 to about 50 atomic percent carbon. In specific implementations, DLG can include about 25 to about 35 atomic percent silicon. Also, in certain implementations, the DLG includes about 20 to about 40 atomic percent oxygen. In specific advantageous implementations the DLG comprises from about 30 to about 36 atomic percent carbon, from about 26 to about 32 atomic percent silicon, and from about 35 to about 41 atomic percent oxygen on a hydrogen free basis. xe2x80x9cHydrogen free basisxe2x80x9d refers to the atomic composition of a material as established by a method such as Electron Spectroscopy for Chemical Analysis (ESCA), which does not detect hydrogen even if large amounts are present in the thin films. (References to compsitional percentages herein refer to atomic percents.)
Thin films made in accordance with the invention may have a variety of light transmissive properties. Thus, depending upon the composition, the thin films may have increased transmissive properties at various frequencies. In specific implementations the thin film is at least 50 percent transmissive to radiation at one or more wavelength from about 180 to about 800 nanometers. In other advantageous implementations the DLG film is transmissive to greater than 70 percent (and more advantageously greater than 90 percent) of radiation at one or more wavelengths from about 180 to about 800 nanometers. High transmissivity is typically preferred because it allows thicker films to be produced without significant reduction in radiation intensity passing through the film.
Regardless of how thick the film is, the DLG typically has an extinction coefficient of less than 0.002 at 250 nm and more typically less than 0.010 at 250 nm. Also, DLG usually has a refractive index greater than 1.4 and sometimes greater than 1.7. Notably, DLG shows low levels of fluorescence, typically very low, and sometimes low enough that it shows no fluorescence. Preferably, DLG""s fluorescence is comparable, nearly equal, or equal to that of pure quartz.
The DLG of the invention can be used for numerous applications. These applications include use on a variety of substrates such as on elastomeric films, on relaxable films such as those disclosed in application Ser. No. 09/519,450, filed concurrently herewith, and incorporated herein by reference, on shrink films, for example to provide a surface treatment to improve wettability of the film, as a substrate for in situ synthesis of oligonucleotides, or as an abrasive surface. The thin films can be used as an internal or external treatment for glass or plastic capillaries, arrays, and biochips. For example, they can be used as an internal surface treatment for surface chemistry modification, or as an external treatment as an alternative to polymer coatings. The good optical properties, high temperature resistance, chemical resistance, and physical durability of DLG films makes them well suited for these purposes. Also, the DLG films can be applied to porous substrates, such as nonwoven cloth, providing further advantageous utility.
The invention is further directed to a method of depositing a diamond-like glass film onto a substrate. The method includes providing a capacitively coupled reactor system having two electrodes in an evacuable reaction chamber. The chamber is partially evacuated, and radio frequency power is applied to one of the electrodes. A carbon and silicon containing source is introduced between the electrodes to form a plasma including reactive species in proximity to the electrodes, and to also form an ion sheath proximate at least one electrode. The substrate is placed within the ion sheath and exposed to the reactive species to form a diamond-like glass on the substrate. The conditions can result in a thin film that includes, for example, a diamond-like structure having on a hydrogen-free basis at least 30 atomic percent carbon, at least 25 atomic percent silicon, and less than 45 atomic percent oxygen. The thin film can be made to a specific thickness, typically from 1 to 10 microns, but optionally less than 1 micron or more than 10 microns.
As used herein, the term xe2x80x9cdiamond-like glassxe2x80x9d (DLG) refers to substantially or completely amorphous glass including carbon and silicon, and optionally including one or more additional component selected from the group including hydrogen, nitrogen, oxygen, fluorine, sulfur, titanium, and copper. Other elements may be present in certain embodiments. The amorphous diamond-like glass films of this invention may contain clustering of atoms to give it a short-range order but are essentially void of medium and long range ordering that lead to micro or macro crystallinity which can adversely scatter radiation having wavelengths of from 180 nm to 800 nm.
As used herein, the term xe2x80x9camorphousxe2x80x9d means a substantially randomly-ordered non-crystalline material having no x-ray diffraction peaks or modest x-ray diffraction peaks. When atomic clustering is present, it typically occurs over dimensions that are small compared to the wavelength of the actinic radiation.
As used herein, the term xe2x80x9cparallel plate reactorxe2x80x9d means a reactor containing two electrodes, wherein the primary mechanism for current flow between the electrodes is capacitive coupling. The electrodes may be asymmetric, meaning that they may be of different size, shape, surface area, etc. and need not necessarily be parallel to each other. One electrode may be grounded, and one electrode may be the reaction chamber itself.
As used herein, the term xe2x80x9cplasmaxe2x80x9d means a partially ionized gaseous or fluid state of matter containing reactive species which include electrons, ions, neutral molecules, free radicals, and other excited state atoms and molecules. Visible light and other radiation are typically emitted from the plasma as the species forming the plasma relax from various excited states to lower, or ground, states. The plasma usually appears as a colored cloud in the reaction chamber.
As used herein, the term xe2x80x9cnegative biasxe2x80x9d means that an object (e.g., an electrode) has a negative electrical potential with respect to some other matter (e.g., a plasma) in its vicinity.
As used herein, the term xe2x80x9cnegative self biasxe2x80x9d, with respect to an electrode and a plasma, means a negative bias developed by application of power (e.g., radio frequency) to an electrode that creates a plasma.
Advantages of the invention will be apparent from the following description, figures, examples, and the appended claims.